If
the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule
13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box ☒.

Note: Schedules
filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See
§ 240.13d-7 for other parties to whom copies are to be sent.

1
The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to
the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided
in a prior cover page.

The information required
on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities
Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject
to all other provisions of the Act (however, see the Notes).

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BIOTECHNOLOGY VALUE FUND, L.P.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

1,677,7351

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

1,677,7351

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,677,7351

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

9.4%1

14

TYPE OF REPORTING PERSON

PN

1
Includes 310,194 American Depositary Shares (“ADSs”), each of which represents one (1) Share (as defined
below).

2

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BIOTECHNOLOGY VALUE FUND II, L.P.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

1,297,7831

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

1,297,7831

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,297,7831

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

7.2%1

14

TYPE OF REPORTING PERSON

PN

1
Includes 198,372 ADSs, each of which represents one (1) Share.

3

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BIOTECHNOLOGY VALUE TRADING FUND OS LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

CAYMAN ISLANDS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

284,6171

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

284,6171

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

284,6171

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

1.6%1

14

TYPE OF REPORTING PERSON

PN

1
Includes 53,195 ADSs, each of which represents one (1) Share.

4

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BVF PARTNERS OS LTD.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

CAYMAN ISLANDS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

284,6171

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

284,6171

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

284,6171

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

1.6%1

14

TYPE OF REPORTING PERSON

CO

1
Includes 53,195 ADSs, each of which represents one (1) Share.

5

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BVF PARTNERS L.P.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

3,630,6621

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

3,630,6621

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

3,630,6621

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

20.2%1

14

TYPE OF REPORTING PERSON

PN, IA

1 Includes
625,000 ADSs, each of which represents one (1) Share.

6

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BVF INC.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

3,630,6621

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

3,630,6621

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

3,630,6621

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

20.2%1

14

TYPE OF REPORTING PERSON

CO

1 Includes
625,000 ADSs, each of which represents one (1) Share.

7

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

MARK N. LAMPERT

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

3,630,6621

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

3,630,6621

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

3,630,6621

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

20.2%1

14

TYPE OF REPORTING PERSON

IN

1 Includes
625,000 ADSs, each of which represents one (1) Share.

8

CUSIP NO. 29604W108

The following constitutes
the Schedule 13D filed by the undersigned (the “Schedule 13D”). The Reporting Persons initially filed a Schedule 13G
with respect to the securities of the Issuer (defined below) pursuant to Rule 13d-1(c) of the Securities Exchange Act of 1934,
as amended (the “Exchange Act”) on January 2, 2018, and filed an amendment thereto. As of July 16, 2018, certain of
the Reporting Persons may be deemed to beneficially own in excess of twenty percent of the outstanding Shares (defined below) of
the Issuer. Accordingly, the Reporting Persons are no longer eligible to report their beneficial ownership with respect to the
securities of the Issuer on Schedule 13G, and in accordance with Rule 13d-1(f) of the Exchange Act, the Reporting Persons are transitioning
to a Schedule 13D.

Item 1.

Security and Issuer.

This statement relates
to Ordinary Shares, nominal value €0.10 per share (the “Shares”), of ERYTECH Pharma S.A., a Société
Anonyome, incorporated under the laws of France (the “Issuer”) and to American Depositary Shares of the Issuer (“ADS”),
each of which represents one Share. The address of the principal executive offices of the Issuer is Bâtiment Adénine,
60 Avenue Rockefeller 69008 Lyon France.

BVF Partners L.P., a Delaware limited partnership (“Partners”), which serves as the
general partner of each of BVF and BVF2, the investment manager of Trading Fund OS, the sole member of Partners OS, and the investment
manager of certain managed accounts (the “Partners Managed Accounts”);

(vi)

BVF Inc., a Delaware corporation, which serves as the general partner of Partners; and

(vii)

Mark N. Lampert, who serves as the sole officer and director of BVF Inc.

Each of the foregoing
is referred to as a “Reporting Person” and collectively as the “Reporting Persons.” Each of the Reporting
Persons is party to that certain Joint Filing Agreement, as further described in Item 6. Accordingly, the Reporting Persons are
hereby filing a joint Schedule 13D.

(c)The
principal business of each of BVF, BVF2, and Trading Fund OS is investing in securities. The principal business of Partners OS
is serving as the general partner of Trading Fund OS. The principal business of Partners is serving as the general partner of each
of BVF and BVF2, the investment manager of Trading Fund OS, the sole member of Partners OS, and the investment manager of the Partners
Managed Accounts. The principal business of BVF Inc. is serving as the general partner of Partners. The principal business of Mr.
Lampert is serving as the sole officer and director of BVF Inc.

(d)No
Reporting Person has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar
misdemeanors).

(e)No
Reporting Person has, during the last five years, been party to a civil proceeding of a judicial or administrative body of competent
jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations
of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to
such laws.

(f)Mr.
Lampert is a citizen of the United States of America.

Item 3.

Source and Amount of Funds or Other Consideration.

The Shares and ADSs
purchased by BVF, BVF2 and Trading Fund OS were purchased with working capital (which may, at any given time, include margin loans
made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted. The aggregate
purchase price of the 1,367,541 Shares beneficially owned by BVF is approximately $20,064,399, including brokerage commissions.
The aggregate purchase price of the 310,194 ADSs beneficially owned by BVF is approximately $7,215,112, including brokerage commissions.
The aggregate purchase price of the 1,099,411 Shares beneficially owned by BVF2 is approximately $15,834,530, including brokerage
commissions. The aggregate purchase price of the 198,372 ADSs beneficially owned by BVF2 is approximately $4,614,133, including
brokerage commissions. The aggregate purchase price of the 231,422 Shares beneficially owned by Trading Fund OS is approximately
$3,350,642, including brokerage commissions. The aggregate purchase price of the 53,195 ADSs beneficially owned by Trading Fund
OS is approximately $1,237,316, including brokerage commissions. The aggregate purchase price of the 307,288 Shares held in the
Partners Managed Accounts is approximately $4,581,049, including brokerage commissions. The aggregate purchase price of the 63,239
ADSs held in the Partners Managed Accounts is approximately $1,470,939, including brokerage commissions.

Item 4.

Purpose of Transaction

The Reporting Persons
purchased the Shares based on the Reporting Persons’ belief that the Shares, when purchased, were undervalued and represented
an attractive investment opportunity. Depending upon overall market conditions, other investment opportunities available to the
Reporting Persons, and the availability of Shares at prices that would make the purchase or sale of Shares desirable, the Reporting
Persons may endeavor to increase or decrease their position in the Issuer through, among other things, the purchase or sale of
Shares on the open market or in private transactions or otherwise, on such terms and at such times as the Reporting Persons may
deem advisable.

10

CUSIP NO. 29604W108

No Reporting Person
has any present plan or proposal which would relate to or result in any of the matters set forth in subparagraphs (a) - (j) of
Item 4 of Schedule 13D except as set forth herein or such as would occur upon or in connection with completion of, or following,
any of the actions discussed herein. The Reporting Persons intend to review their investment in the Issuer on a continuing basis.
Depending on various factors including, without limitation, the Issuer’s financial position and investment strategy, the
price levels of the Shares, conditions in the securities markets and general economic and industry conditions, the Reporting Persons
may in the future take such actions with respect to their investment in the Issuer as they deem appropriate including, without
limitation, engaging in communications with management and the Board of the Issuer, engaging in discussions with stockholders of
the Issuer and others about the Issuer and the Reporting Persons’ investment, making proposals to the Issuer concerning changes
to the capitalization, ownership structure, board structure (including board composition) or operations of the Issuer, purchasing
additional Shares, selling some or all of their Shares, engaging in short selling of or any hedging or similar transaction with
respect to the Shares, or changing their intention with respect to any and all matters referred to in Item 4.

Item 5.

Interest in Securities of the Issuer.

(a)The
aggregate percentage of Shares reported owned by each person named herein is based on 17,940,035 Shares outstanding as of June
30, 2018, as disclosed by the Issuer.

As of the close of
business on July 18, 2018, (i) BVF beneficially owned 1,677,735 Shares, representing percentage ownership of approximately 9.4%
of the Shares outstanding, (ii) BVF2 beneficially owned 1,297,783 Shares, representing percentage ownership of approximately 7.2%
of the Shares outstanding, (iii) Trading Fund OS beneficially owned 284,617 Shares, representing percentage ownership of approximately
1.6% of the Shares outstanding and (iv) 370,527 Shares were held in the Partners Managed Accounts, representing percentage ownership
of approximately 2.1% of the Shares outstanding.

Partners OS, as the
general partner of Trading Fund OS, may be deemed to beneficially own the 284,617 Shares beneficially owned by Trading Fund OS,
representing percentage ownership of approximately 1.6% of the Shares outstanding.

Partners, as the general
partner of BVF and BVF2, the sole member of Partners OS, and the investment manager of Trading Fund OS and the Partners Managed
Accounts, may be deemed to beneficially own the 3,630,662 Shares beneficially owned in the aggregate by BVF, BVF2, Trading Fund
OS, and the Partners Managed Accounts, representing percentage ownership of approximately 20.2% of the Shares outstanding.

BVF Inc., as the general
partner of Partners, may be deemed to beneficially own the 3,630,662 Shares beneficially owned by Partners, representing percentage
ownership of approximately 20.2% of the Shares outstanding.

Mr. Lampert, as a
director and officer of BVF Inc., may be deemed to beneficially own the 3,630,662 Shares beneficially owned by BVF Inc., representing
percentage ownership of approximately 20.2% of the Shares outstanding.

(b)Each
of BVF, BVF2, and Trading Fund OS, shares with Partners voting and dispositive power over the Shares each such entity beneficially
owns. Trading Fund OS, shares with Partners OS, voting and dispositive power over the Shares beneficially owned by Trading Fund
OS. Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the 3,630,662 Shares they may be deemed to beneficially
own with BVF, BVF2, Trading Fund OS, Partners OS and the Partners Managed Accounts.

(c)Schedule
A annexed hereto lists all transactions in securities of the Issuer during the past sixty days by the Reporting Persons. All of
such transactions were effected in the open market, except as otherwise noted.

(d)No
person other than the Reporting Persons is known to have the right to receive, or the power to direct the receipt of dividends
from, or proceeds from the sale of, the Shares.

(e)Not
applicable.

11

CUSIP NO. 29604W108

Item 6.

Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

On July 18, 2018,
the Reporting Persons entered into a Joint Filing Agreement in which the Reporting Persons agreed to the joint filing on behalf
of each of them of statements on Schedule 13D, with respect to securities of the Issuer, to the extent required by applicable law.
A copy of this agreement is attached hereto as Exhibit 99.1 hereto and is incorporated herein by reference.

Partners is the general
partner of each of BVF and BVF2 pursuant to limited partnership agreements which authorize Partners, among other things, to invest
the funds of BVF and BVF2 in the Shares and other securities and to vote, exercise or convert and dispose of such securities. Pursuant
to such limited partnership agreements, Partners is entitled to receive fees based on assets under management and allocations based
on realized and unrealized gains on such assets.

Partners is the sole
member of Partners OS and the investment manager of Trading Fund OS, pursuant to an investment management agreement which authorizes
Partners, among other things, to invest the funds of Trading Fund OS in the Shares and other securities and to vote, exercise or
convert and dispose of such securities. Pursuant to such investment management agreement, Partners is entitled to receive fees
based on assets under management and allocations based on realized and unrealized gains on such assets

Pursuant to investment
management agreements with certain of the Partners Managed Accounts, Partners and BVF Inc. have authority, among other things,
to invest funds of certain of the Partners Managed Accounts in the Shares and other securities and to vote, exercise or convert
and dispose of such securities. Pursuant to such investment management agreements, Partners and BVF Inc. receive fees based on
realized and unrealized gains thereon.

Other than as described
herein, there are no contracts, arrangements, understandings or relationships among the Reporting Persons, or between the Reporting
Persons and any other person, with respect to the securities of the Issuer.

After reasonable inquiry
and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement
is true, complete and correct.

Dated: July 18, 2018

BIOTECHNOLOGY VALUE FUND, L.P.

BVF INC.

By:

BVF Partners L.P., its general partner

/s/ Mark N. Lampert

By:

BVF Inc., its general partner

By:

Mark N. Lampert

President

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

/s/ Mark N. Lampert

MARK N. LAMPERT

BIOTECHNOLOGY VALUE FUND II, L.P.

By:

BVF Partners L.P., its general partner

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

BVF PARTNERS L.P.

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

BVF PARTNERS OS LTD.

By:

BVF Partners L.P., its sole member

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

Biotechnology Value Trading Fund OS LP

By:

BVF Partners L.P., its investment manager

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

13

CUSIP NO. 29604W108

SCHEDULE A

Transactions in the Securities
of the Issuer During the Past Sixty Days

Class
of
Security

Securities
Purchased / (Sold)

Price
(€)

Date
of
Purchase / Sale

BIOTECHNOLOGY VALUE FUND, L.P.

Ordinary Shares

26,266

16.4000

05/29/2018

Ordinary Shares

154,490

9.6620

06/28/2018

Ordinary Shares

729,852

9.6000

06/29/2018

BIOTECHNOLOGY VALUE FUND II, L.P.

Ordinary Shares

23,673

16.4000

05/29/2018

Ordinary Shares

113,818

9.6620

06/28/2018

Ordinary Shares

487,824

9.6000

06/29/2018

Ordinary Shares

155,974

9.4000

07/16/2018

BIOTECHNOLOGY VALUE TRADING FUND
OS LP

Ordinary Shares

61

16.4000

05/29/2018

Ordinary Shares

17,379

9.6620

06/28/2018

Ordinary Shares

136,250

9.6000

06/29/2018

BVF PARTNERS L.P. (THROUGH THE PARTNERS
MANAGED ACCOUNTS)

Ordinary Shares

(7,769)

15.8382

06/11/2018

Ordinary Shares

(3,030)

15.8848

06/12/2018

Ordinary Shares

(3,836)

15.8819

06/13/2018

Ordinary Shares

(5,153)

15.8490

06/14/2018

Ordinary Shares

(3,354)

15.7550

06/15/2018

Ordinary Shares

(934)

15.5097

06/19/2018

Ordinary Shares

(15,498)

15.6209

06/20/2018

Ordinary Shares

5,444

9.6620

06/28/2018

Ordinary Shares

8,869

9.6620

06/28/2018

Ordinary Shares

54,674

9.6000

06/29/2018

Ordinary Shares

91,400

9.6000

06/29/2018

Ordinary Shares

15,597

9.4000

07/16/2018

Ordinary Shares

21,864

9.4000

07/16/2018

Exhibit 99.1

JOINT FILING AGREEMENT

In accordance with
Rule 13d-1(k)(1)(iii) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing
on behalf of each of them of a Statement on Schedule 13D dated July 18, 2018 (including amendments thereto) with respect to the
Ordinary Shares, nominal value €0.10 per share, of ERYTECH Pharma S.A. This Joint Filing Agreement shall be filed as an Exhibit
to such Statement.